Sunan an-Nasa'i, Volume 5, Book 45, Hadith 4820 (DarusSalam) ⓘ
Hamal bin Malik said: "The Messenger of Allah ruled that a slave (should be given as Diyah) for a fetus." Tawus said: "A horse would do in place of a slave."
أَخْبَرَنَا قُتَيْبَةُ، قَالَ حَدَّثَنَا حَمَّادٌ، عَنْ عَمْرٍو، عَنْ طَاوُسٍ، أَنَّ عُمَرَ، اسْتَشَارَ النَّاسَ فِي الْجَنِينِ فَقَالَ حَمَلُ بْنُ مَالِكٍ قَضَى رَسُولُ اللَّهِ صلى الله عليه وسلم فِي الْجَنِينِ غُرَّةً . قَالَ طَاوُسٌ إِنَّ الْفَرَسَ غُرَّةٌ .
also referenced under: Hadith 4816 (Reference) & Book 45, Hadith 111 (In-Book)